CVE-2021-34836 in Foxit
Summary
by MITRE • 08/04/2021
This vulnerability allows remote attackers to execute arbitrary code on affected installations of Foxit PDF Reader 11.0.0.49893. User interaction is required to exploit this vulnerability in that the target must visit a malicious page or open a malicious file. The specific flaw exists within the handling of Annotation objects. The issue results from the lack of validating the existence of an object prior to performing operations on the object. An attacker can leverage this vulnerability to execute code in the context of the current process. Was ZDI-CAN-14017.
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Analysis
by VulDB Data Team • 08/08/2021
CVE-2021-34836 represents a critical remote code execution vulnerability in Foxit PDF Reader version 11.0.0.49893 that demonstrates a classic object validation flaw in the PDF parsing engine. This vulnerability falls under the CWE-476 category, specifically addressing null pointer dereference conditions where the application fails to validate object existence before attempting operations on them. The flaw manifests within the annotation object handling mechanism, which is a fundamental component of PDF documents used for adding comments, highlights, and interactive elements to documents. When processing maliciously crafted PDF files, the reader's annotation parser does not properly validate whether referenced objects exist in memory before attempting to access their properties or methods, creating an exploitable condition that can be leveraged by remote attackers.
The attack scenario requires user interaction through either visiting a malicious webpage that serves a crafted PDF file or opening a specially prepared malicious document, making this vulnerability particularly dangerous in phishing campaigns and drive-by download attacks. The exploitation process involves crafting an annotation object that references a non-existent or improperly initialized object within the PDF structure, causing the application to dereference a null pointer and subsequently execute arbitrary code within the context of the current process. This privilege escalation occurs because PDF readers typically run with the same privileges as the user who opened the document, potentially allowing attackers to gain access to sensitive system resources or execute malicious payloads with user-level permissions.
The operational impact of this vulnerability extends beyond simple code execution, as it can enable attackers to perform various malicious activities including data exfiltration, system reconnaissance, and deployment of additional malware. The vulnerability's presence in a widely used PDF reader application creates a significant risk for enterprise environments where users frequently open PDF documents from untrusted sources. Security researchers have documented similar patterns in other PDF processing libraries where improper object validation leads to memory corruption vulnerabilities, making this issue consistent with established attack vectors in the cybersecurity landscape. The vulnerability's classification aligns with ATT&CK technique T1203, which covers exploitation for privilege escalation through application vulnerabilities, and T1566, which addresses social engineering techniques involving malicious document delivery.
Organizations should prioritize immediate patching of Foxit PDF Reader installations to address this vulnerability, as the lack of input validation creates a persistent risk for remote code execution attacks. The mitigation strategy should include implementing network-level controls such as web application firewalls and content filtering systems to block access to known malicious PDF sources, alongside user education programs to reduce the likelihood of successful social engineering attacks. Additionally, security teams should consider implementing sandboxing mechanisms for PDF processing and monitoring for unusual process behavior that might indicate exploitation attempts. The vulnerability underscores the critical importance of proper object validation in software development practices and highlights the necessity of regular security assessments for commonly used applications. Organizations should also consider implementing automated patch management systems to ensure timely deployment of security updates and maintain comprehensive incident response procedures that account for potential exploitation of this class of vulnerability.